I've search the forums and can find loads of aircon issues but nothing that sounds quite like mine! I've got a early 2003 MCS. For the last year or two it's made the following noise - a sort of whooshing/gurgling type sound which seems to be accompanied by something that sounds like a rough bearing rotating (the sort of graunching sound). The sounds are coming from the engine bay (well centre console when I'm in the car). It's quite hard to track from the bonnet though - harder to hear. It's quite loud - it's such that it's probably louder than the engine - i.e pretty much the loudest sound the car makes.

Was in the dealer last week and they couldn't spot anything - they claimed they didn't hear it which I found odd. After reading some of the posts here, I thought I wonder if it's the aircon. I can reproduce the noise by starting the car with the aircon off and from cool. Start the aircon, the noises start a few seconds after. Turn off the aircon - noises continue! It definitely seems to be related to turning the a/c on but I'm not sure why it doesn't disappear when I turn it off again. It's making these noises even in British winter type of temperatures. I do tend to keep the a/c on pretty much all the time to prevent misting up.

Don't know if it's related but the engine fan comes on relatively quickly and can often run full speed for 15 minutes after I stop, even on a short-ish journey.